Many of the currently available surgical approaches for closing openings and repairing defects in anatomical lumens and tissues (e.g., blood vessels), septal defects, and other types of anatomical irregularities and defects are highly invasive. Surgical methods for clipping brain aneurysms, for example, require opening the skull, cutting or removing overlying brain tissue, clipping and repairing the aneurysm from outside the blood vessel, and then reassembling tissue and closing the skull. Surgical techniques for repairing septal defects are also highly invasive. The risks related to anesthesia, bleeding, and infection associated with these types of procedures are high, and tissue that is affected during the procedure may or may not survive and continue functioning.
Minimally invasive surgical techniques have been developed to place occlusive devices within or across an opening or cavity in the body, such as in the vasculature, spinal column, fallopian tubes, bile ducts, bronchial and other air passageways, and the like. In general, an implantable device is guided along a delivery catheter and through a distal opening of the catheter using a pusher or delivery wire to deploy the device at a target site in the vasculature. Once the occlusive device has been deployed at the target site, it is detached from the pusher mechanism without disturbing placement of the occlusive device or damaging surrounding structures.
Minimally invasive techniques are also highly desirable for treating aneurysms. In general, the minimally invasive therapeutic objective is to prevent material that collects or forms in the cavity from entering the bloodstream and to prevent blood from entering and collecting in the aneurysm. This is often accomplished by introducing various materials and devices into the aneurysm. One class of embolic agents includes injectable fluids or suspensions, such as microfibrillar collagen, various polymeric beads, and polyvinylalcohol foam. Polymeric agents may also be cross-linked to extend their stability at the vascular site. These agents are typically deposited at a target site in the vasculature using a catheter to form a solid space-filling mass. Although some of these agents provide for excellent short-term occlusion, many are thought to allow vessel recanalization due to their absorption into the blood. Other materials, such as hog hair and suspensions of metal particles, have also been proposed and used to promote occlusion of aneurysms. Polymer resins, such as cyanoacrylates, are also employed as injectable vaso-occlusive materials. These resins are typically mixed with a radiopaque contrast material or are made radiopaque by the addition of a tantalum powder. Accurate and timely placement of these mixtures is crucial and very difficult because it is difficult or impossible to control them once they have been placed in the blood flow.
Implantable vaso-occlusive metallic structures are also well known and commonly used. Many conventional vaso-occlusive devices have helical coils constructed from a shape memory material or noble metal that forms a desired coil configuration upon exiting the distal end of a delivery catheter. The function of the coil is to fill the space formed by an anatomical defect and to facilitate the formation of an embolus with the associated allied tissue. Multiple coils of the same or different structures may be implanted serially in a single aneurysm or other vessel defect during a procedure. Implantable framework structures are also used in an attempt to stabilize the wall of the aneurysm or defect prior to insertion of filling material such as coils.
Techniques for delivering conventional metallic vaso-occlusive devices to a target site generally involve a delivery catheter and a detachment mechanism that detaches the devices, such as a coil, from a delivery mechanism after placement at the target site. For example, a microcatheter can be initially steered through the delivery catheter into or adjacent to the entrance of an aneurysm either with or without a steerable guidewire. If a guidewire is used, it is then withdrawn from the microcatheter lumen and replaced by the implantable vaso-occlusive coil. The vaso-occlusive coil is advanced through and out of the microcatheter and thus deposited within the aneurysm or other vessel abnormality. It is crucial to accurately implant such vaso-occlusive devices within the internal volume of a cavity and to maintain the device within the internal volume of the aneurysm. Migration or projection of a vaso-occlusive device from the cavity may interfere with blood flow or nearby physiological structures and poses a serious health risk.
In addition to the difficulties of delivering implantable occlusion devices, some types of aneurysms are challenging to treat because of structural features of the aneurysm or because of particularities of the site. Wide-neck aneurysms, for example, are known to present particular difficulty in the placement and retention of vaso-occlusive coils. Aneurysms at sites of vascular bifurcation are another example where the anatomical structure poses challenges to methods and devices that are effective in treating the typical sidewall aneurysms.
In view of such challenges, implanting conventional embolic coils, other structures, or materials in the internal space of an aneurysm has not been an entirely satisfactory surgical approach. The placement procedure may be arduous and lengthy because it often requires implanting multiple devices, such as coils, serially in the internal space of the aneurysm. Higher risks of complication from such sources as anesthesia, bleeding, thromboembolic events, procedural stroke, and infection are associated with such longer procedures. Moreover, because placement of structures in the internal space of an aneurysm does not generally completely occlude the opening, recanalization of the original aneurysm may occur, and debris and occlusive material may escape from within the aneurysm to create a risk of stroke or vessel blockage. Blood may also flow into the aneurysm and other blood vessel irregularities after the placement of embolic devices, which may increase the risks of complication and further enlargement of the aneurysm.
Despite the numerous conventional devices and systems available for implanting embolic materials in an aneurysm and for occluding physiological defects using minimally invasive techniques, these procedures remain risky and rarely restore the physiological structure to its normal, healthy condition. It is also challenging to position conventional implantable devices during deployment, prevent shifting or migration of such devices after deployment, and preserve blood flow in neighboring vessels following after deployment.